1. Field
Exemplary embodiments of the present invention relate generally to a semiconductor design technology and, more particularly, to an image sensing device and a method for driving the same.
2. Description of the Related Art
Image sensing devices capture images using photosensitive properties of semiconductors. Image sensing devices are often classified into charge-coupled device (CCD) image sensors and complementary metal-oxide semiconductor (CMOS) image sensors. CMOS image sensors allow for both analog and digital control circuits to be directly realized on a single integrated circuit (IC), making CMOS image sensors the most widely used type of image sensor.
Image sensing devices include a ramp signal generation circuit for generating a ramp signal required when a voltage level of a pixel signal is determined. The ramp signal generation circuit is often classified into a ramp signal generation circuit based on a variable current and a ramp signal generation circuit based on a variable resistance. The ramp signal generation circuit based on the variable current controls a slope of the ramp signal by controlling a current amount when generating the ramp signal. The ramp signal generation circuit based on the variable resistance controls the slope of the ramp signal by controlling a resistance value when generating the ramp signal. The slope of the ramp signal is related to an analog gain. The ramp signal generation circuit based on the variable resistance is insensitive to a device noise as compared with the ramp signal generation circuit based on the variable current.
In addition, image sensing devices include a noise compensation circuit for offsetting a noise component reflected in a pixel signal. The noise component may be a pixel power noise included in a driving voltage used for generating the pixel signal. The noise compensation circuit senses the noise component based on the driving voltage and reflects the sensed noise component in the ramp signal. In this case, the noise component reflected in the pixel signal and the noise component reflected in the ramp signal through a latter-side circuit are offset by each other.